The present invention relates to delivering multicast/broadcast services (MBS) in a half frequency division duplex (H-FDD) wireless communication system and, more particularly, to delivering MBS over H-FDD in a way that minimizes MBS bandwidth allocation and maintains appropriate balance between two H-FDD mobile device groups.
Institute of Electrical and Electronics Engineers Standard 802.16 (IEEE 802.16) for wireless metropolitan area networks, commonly known as WiMAX (an acronym for Worldwide Interoperability for Microwave Access), was originally designed for time division duplex operation in which a single frequency is used for both transmission and reception. However, much of the wireless spectrum made available for WiMAX by governments has paired frequencies for use in a frequency division duplex (FDD) operation wherein one frequency is used for transmission while the other is used for reception. Thus, WiMAX is being adapted to support FDD.
Unfortunately, deployment of WiMAX systems with full support for FDD may often be cost prohibitive since the mobile devices in such systems must be able to transmit and receive simultaneously. To reduce the cost of deployment of WiMAX systems on paired frequencies, many mobile devices will instead support H-FDD. Referring to FIG. 1, an exemplary H-FDD system is shown. The mobile devices are divided into two groups: Group 1 120 and Group 2 130. A base station 110 simultaneously transmits data to one or more mobile devices in one group on a downlink frequency while receiving data from a mobile device in the other group on an uplink frequency. The mobile devices do not simultaneously transmit and receive data. Instead, the mobile devices switch between the downlink frequency and the uplink frequency to receive and transmit data in sequence. Mobile devices in Group 1 120 transmit data to base station 110 on an uplink frequency while mobile devices in Group 2 receive data from base station 110 on a downlink frequency, and vice versa.
These operations are shown in greater detail in FIG. 2. The H-FDD system includes a downlink frequency on which mobile devices receive data from base station 110 and an uplink frequency on which mobile devices transmit data to base station 110. Base station 110 transmits on the downlink frequency a Group 1 allocation map 210 that allocates sections of Group 1 downlink bandwidth 220 and Group 1 uplink bandwidth 250 to individual mobile devices in Group 1 120. Base station 110 also transmits on the downlink frequency a Group 2 allocation map 230 that allocates sections of Group 2 downlink bandwidth 240 and Group 2 uplink bandwidth 260 to individual mobile devices in Group 2 130. Mobile devices in Group 1 120 decode Group 1 allocation map 210 to determine their respectively allocated sections of Group 1 downlink bandwidth 220 and uplink bandwidth 250. Similarly, mobile devices in Group 2 130 decode Group 2 allocation map 230 to determine their respectively allocated sections of Group 2 downlink bandwidth 240 and uplink bandwidth 260. The mobile devices proceed to decode data transmitted by base station 110 during their respectively allocated sections of downlink bandwidth and transmit data to base station 110 during their respectively allocated sections of uplink bandwidth.
One unresolved issue surrounding use of H-FDD with WiMAX is how to best deliver MBS. MBS are streaming services defined in WiMAX over which a base station can deliver multimedia broadcasts and multicasts (e.g. television station feeds) simultaneously to many mobile devices. One approach to delivering MBS over H-FDD that has been suggested is to force all mobile devices that subscribe to MBS into a single group. This approach is illustrated in FIG. 3. All mobile devices subscribing to MBS are placed in Group 2. Base station 110 transmits on the downlink frequency a Group 2 allocation map 310 that allocates a Group 2 downlink bandwidth section 320 to MBS. Mobile devices in Group 2 that subscribe to MBS decode Group 2 allocation map 310 and identify section 320 as allocated to MBS, and also identify their respectively allocated individual sections of Group 2 downlink bandwidth and uplink bandwidth. These mobile devices in Group 2 proceed to decode MBS data transmitted by base station 110 during section 320, and also decode data transmitted by base station 110 during their respectively allocated individual sections of downlink bandwidth and transmit data to base station 110 during their respectively allocated individual sections of uplink bandwidth. While this approach only requires allocation of MBS bandwidth to a single group, a high rate of subscription to MBS can create a lack of group balance. In the example shown, if most of the mobile devices in the H-FDD system subscribe to MBS, Group 2 will be disproportionately large relative to Group 1. Compounding the problem, less downlink bandwidth will be available for individual allocation to members of Group 2 than members of Group 1. This can severely complicate allocation of bandwidth by the base station scheduler.
Another approach to delivering MBS over H-FDD that has been suggested is to allocate downlink bandwidth sections to MBS within both Group 1 and Group 2. This approach is illustrated in FIG. 4. Mobile devices subscribing to MBS are divided between Group 1 120 and Group 2 130. Base station 110 transmits on the downlink frequency a Group 1 allocation map 410 that allocates a Group 1 downlink bandwidth section 420 to MBS. Mobile devices in Group 1 that subscribe to MBS decode Group 1 allocation map 410 and identify section 420 as having been allocated to MBS, and also identify their respectively allocated individual sections of Group 1 downlink bandwidth and uplink bandwidth. Mobile devices in Group 1 then decode MBS data transmitted by base station 110 during section 420, and also decode data transmitted by base station 110 during their respectively allocated individual sections of downlink bandwidth and transmit data to base station 110 during their respectively allocated individual sections of uplink bandwidth. Similarly, base station 110 transmits on the downlink frequency a Group 2 allocation map 430 that allocates a Group 2 downlink bandwidth section 440 to MBS. Mobile devices in Group 2 that subscribe to MBS decode Group 2 allocation map 430 and identify section 440 as having been allocated to MBS, and also identify their respectively allocated individual sections of Group 2 downlink bandwidth and uplink bandwidth. Mobile devices in Group 2 then decode MBS data transmitted by base station 110 during section 440, and also decode data transmitted by base station 110 during their respectively allocated individual sections of downlink bandwidth and transmit data to base station 110 during their respectively allocated individual sections of uplink bandwidth. This approach allows group balance to be maintained; however, it doubles the bandwidth allocation to MBS. This reduces the amount of downlink bandwidth available for individual allocation and can delay important transmissions.